1. Field of the Invention
This invention relates to fully and partially automated vehicular mechanical transmission systems of the type requiring sensing of transmission neutral conditions. In particular, the present invention relates to a control method/system for verifying a sensed transmission neutral condition in an at least partially automated mechanical transmission system.
2. Description of the Prior Art
Fully and partially automated mechanical transmission systems intended for vehicular use are well known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,648,290; 4,595,986; 4,850,236; 5,053,959; 5,109,721; 5,261,288 and 5,315,218, the disclosures of which are incorporated herein by reference. In these types of systems, it is typically important to achieve and to sense transmission neutal conditions, such as, for example, when using engine fueling/braking control to achieve synchronous conditions for engaging a target gear ratio.
The prior art automated transmission systems typically utilized electric, electro-mechanical, electro-hydraulic or electro-pneumatic type actuators to operate a plurality of generally parallel shift rails or a single shift shaft mechanism, or the like, through an X-Y mechanism and/or a plurality of linear actuators. Shift mechanisms of this type may be seen by reference to U.S. Pat. Nos. 4,445,393; 4,873,881; 4,899,607; 4,920,815; RE 34,260; 4,945,484 and 5,000,060, the disclosures of which are incorporated herein by reference.
Axially movable jaw clutch members are selectively axially positioned by shift yokes (also called shift forks) carried by shift shafts or block mechanisms, which are axially positioned by shift fingers, pistons and the like. As it is difficult to provide sensors at the transmission jaw clutch mechanisms, jaw clutch position is typically inferred from sensors located in the actuators, which sense the position of shift shafts, shift fingers, actuator pistons and the like. As the forces required to move the jaw clutch members into and/or out of positive engagement may be considerable, such as, for example, when shifting to neutral under torque lock conditions, deflection of shift yokes and/or other members may cause the actual position of the monitored jaw clutch member to be different from that inferred by the sensor.
By way of example, it has been observed that under loaded conditions, a properly operating sensor in the actuator mechanism may indicate that a jaw clutch has disengaged while the jaw clutch is actually sufficiently positively engaged to allow the transmission to transfer torque from the vehicle engine to the vehicle drive wheels. This may result in a very disconcerting situation for the vehicle operator if torque is then applied to the transmission input shaft while attempting to synchronize by use of increased engine fueling, application of an engine brake or input shaft brake, etc.
Prior art controls have had fault-sensing/fault-tolerant logics wherein faulty neutral sensors were identified and fault-tolerant logic was adopted. See aforementioned U.S. Pat. No. 4,945,484; see also, U.S. Pat. No. 4,702,127, the disclosures of which are incorporated herein by reference.
The prior art control methods/systems were not totally satisfactory, as deflections and the like may cause incorrect inferences of clutch conditions, even with non-faulty sensor operation and/or relied on waiting for and/or causing a predetermined speed difference across the suspected disengaged jaw clutch, which may be time-consuming and which may not occur even if the jaw clutch is disengaged and/or may not distinguish between incorrect neutral position indications resulting from a faulty sensor condition and incorrect neutral positions resulting from a deflection condition.